This image released by 20th Century Fox shows Ansel Elgort, right, and Shailene Woodley appear in a scene from "The Fault In Our Stars." (AP Photo/20th Century Fox, James Bridges)

All of these young-adult books and movies are pretty girl-dominated affairs, no matter how many cute guy vampires, werewolves and dystopian future superhunks they might have in them.

Don’t tell that to Ansel Elgort, though. Today he goes toe-to-toe ... wait, that’s a bad choice of phrase. Let’s say he at least truly co-stars with Shailene Woodley in the adaptation of John Green’s phenomenal best-seller “The Fault in Our Stars.” To be honest, he dominates many of their scenes.

While you’re at it, don’t tell Elgort he’s about to become the prince of young adult movies, either.

“This one is more realistic than most stories in this sector,” the 6-foot-4-inch, 20-year-old New Yorker says of the tale about two cancer-stricken teenagers who fall in love.

“The whole pat line of something being ‘young adult,’ I don’t always love it because sometimes it can be limiting. It says, ‘OK, this is for young people but not older people.’

“This is a really universal story,” he continues. “It has a lot of messages that are important to people growing up, but I think to all people as well. It also is a very honest story about illness, which is rare. Very often, stories that have cancer as an element are all about cancer, and about a healthy person learning lessons from a sick person. That’s not very realistic, and it kind of stupidly puts sick people down.

“What’s beautiful about this book is that it says that everyone’s life is as important as everyone else’s, and it’s about finding the meaning in the life that you’re given.”

Elgort’s Gus Waters, in remission but minus the lower portion of a leg, meets Woodley’s Hazel Grace Lancaster at an Indiana cancer kids support group meeting. He likes her looks — even the tube connecting her nostrils to the oxygen tank that she hauls around wherever she goes — and her sweetly sarcastic attitude. He immediately comes on to her with an upbeat, outgoing personality.

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The huge, passionate fan base for Green’s novel is palpably more stoked for the movie than the one for the last young-adult adaptation Elgort and Woodley made together, “Divergent,” in which he played a much smaller role as her character’s brother. Since its publication in early 2012, “Fault” has spent 119 consecutive weeks on the New York Times best-seller list (46 at its top).

The film’s trailer has had more than 16 million hits online, and Elgort reports that a prerelease cast appearance tour drew 10 times the attendance per stop as a similar “Divergent” tour did.

Most of the other kids in the film’s support group were actual young cancer patients. Woodley and Elgort — a veteran of more than 50 stage productions who only made his movie debut in last year’s remake of “Carrie” — learned from them that Green was right about his characters: that they didn’t define themselves by their disease.

The main inspiration for his performance, however, was his movie “leg double,” Tanner Boatwright, a young man who’d lost his limb in a hunting accident.

“I spent a lot of time with Tanner, who at 16 went through the whole process of getting a prosthetic and all of that stuff,” Elgort says. “I really saw how much confidence he gained from it, actually, because of overcoming something. That was something that I could really put into Gus, because he’s so overly confident.”

It’s a bravura performance — and one Elgort was acutely aware had to be bold yet carefully judged.

“A lot of actors are very big on being subtle, not doing too much and making sure they’re being realistic and genuine,” he notes. “But if I were to be subtle with Augustus, he would be boring and the movie would be boring. If me and Shailene didn’t bring the characters to life the way they are in the book, the movie was going to suck.

“So that was definitely a challenge at first. This was only my third film at the time, but after seven years in theater I was comfortable going a little bit big. At times, the director (Josh Boone, “Stuck in Love”) would say ‘pull back,’ but it was important to make Gus over-the-top and theatrical at times.”

Performing all this in front of a familiar face was invaluable.

“Shailene is a really amazing actress and it was really great working opposite her,” he says. “Us doing ‘Divergent’ together was really helpful because we became very close, and then we were able to be comfortable with each other doing this movie. Which was important, because they’re close roles, and at times it could definitely be awkward if we weren’t comfortable with each other.”

Named for photographer Ansel Adams, Elgort is the son of legendary fashion photographer Arthur Elgort and opera producer Grethe Barrett Holby. The artistic parents supported, without pushing, their son, who became involved in musical theater by the age of 9.

Elgort had no desire to become a child star, though, and waited until adulthood to take that step. He also has a passion for singing and composes electronic dance music as Ansolo.

And yes, he plays basketball every day.

Elgort and Woodley are now working on the “Divergent” sequel “Insurgent,” and waiting to see precisely how well the “Fault” movie is received.

“It’s a beautiful story and it’s not very sentimental, which is a nice thing, too,” he says, at least satisfied with the job that’s done.